other
它 centers on the concept of otherness: something separate, different, or not the self. The meaning 'other' is the core idea.
它 originally depicted a snake, and the character was later borrowed to mean 'other'. The modern form combines 宀 (roof) and 匕 (spoon), but these components are not historically related to the original snake pictograph.
Under a roof (宀), a spoon (匕) is set aside for someone else. That spoon is for the other person, not you.
For タ, imagine a tag on the other spoon under the roof: tag -> タ, marking it as belonging to another.